Regioselectivity and Network Structure of Difunctional Alkyl-Substituted Aromatic Amine-Based Polybenzoxazines

The regioselectivity of the benzoxazine polymerization in aromatic amine-based polybenzoxazines is investigated through systematic manipulation of the monomer chemistry. The network structures of the cured materials are elucidated by FTIR and GC/MS. Selectively protecting or activating sites on the pendant aromatic ring toward electrophilic aromatic substitution with alkyl groups allows a series of materials to be developed which contain a varying amount of phenolic Mannich bridges, arylamine Mannich bridges, and methylene linkages. Activation of sites on the pendant rings by methyl substituent groups lowers the peak exotherm temperature by up to 45 °C. Temperature-modulated differential scanning calorimetry shows that in some of these materials the development of the glass transition temperature exceeds that of the curing temperature.